The invention relates to a measuring assembly comprising
a sensor module containing at least one sensor for sensing physical measured variables and for each sensor an analog/digital converter for digitizing the analog measurement signal furnished by the sensor as well as a non-volatile digital memory in which sensor-specific configuration data are stored, and
an analyzer module connected to the sensor module by a digital interface and means for digitally processing the digitized measurement data furnished by the sensor module, means for outputting the processed measurement data and power supply means.
Measuring assemblies of this kind enable the sensor signals in the sensor module to be digitized as near as possible to the sensor and permit further processing such as compensating and converting the measurement results into a form suitable for outputting in the analyzer module separate from the sensor module, as a result of which the noise immunity and signal stability of the measuring assembly are enhanced. Storing the sensor characteristic data such as sensitivity and temperature coefficient as a function of the object concerned in a non-volatile digital memory directly at the sensor makes it easier for the manufacturer to speed up delivery by stocking prefabricated calibrated sensor and analog modules for a plurality of measurement results and licenced options. In addition, repairs or re-ranging the assembly can be implemented without delay in-situ without repeat factory recalibration.
In known measuring assemblies of this kind a bidirectional serial periphery bus controlled by the microcontroller of the analyzer module usually serves as the interface between the sensor module and the analyzer module. The microcontroller addresses via this bus the components of the sensor module, such as the analog/digital converter and the non-volatile digital memory, configurates the sensor module, reads the memorized data and retrieves the measured variables. The program code required for this is stored in the analyzer module, the same applying to the configuration data required. Accordingly, changing the sensor module also necessitates, as a rule, changes in the analyzer module.
Measuring assemblies of the cited kind are usually subject to the requirement that all connecting leads for power supply, measurement signal transfer, communication etc are designed floating relative to the casing. However, to minimize noise being coupled into the sensor and for satisfying specific safety requirements it would be of advantage to directly connect the sensor to the casing. Although these two conflicting requirements could be satisfied by high-potential DC decoupling the sensor module from the analyzer module, the bidirectional serial interfaces needed in known measuring assemblies do not lend themselves to DC decoupling or only by involving a lot of trouble.
It is thus the object of the invention to define a measuring assembly of the aforementioned kind which permits simple replacement of the sensor module without having to change the analyzer module and zero-potential DC decoupling of the sensor module from the analyzer module by simple means and at little expense.
In accordance with the invention this object is achieved in a measuring assembly comprising
a sensor module containing at least one sensor for sensing physical measured variables and for each sensor an analog/digital converter for digitizing the analog measurement signal furnished by the sensor as well as a non-volatile digital memory in which sensor-specific configuration data are stored, and
an analyzer module connected to the sensor module by a digital interface and means for digitally processing the digitized measurement data furnished by the sensor module, means for outputting the processed measurement data and power supply means, wherein
the digital interface is a unidirectional serial interface configured for transferring digital data from the sensor module to the analyzer module,
the non-volatile digital memory in the sensor module contains configuration data for initializing the sensor module as well as the program code and coefficients for processing the digitized measurement data in the analyzer module and
the sensor module contains a control circuit which
immediately on power up of the sensor module prompts readout of the data stored in the non-volatile digital memory, initializes the sensor module by the configuration data readout and transfer of the memorized data readout via the serial interface to the analyzer module and
on completion of transfer of the memorized data prompts transfer of one data block each containing the digitized measurement data via the serial interface to the analyzer module at regular intervals in time without needing to be requested.
In the measuring assembly in accordance with the invention all sensor-specific data including the configuration data and the program code needed for processing the measurement data are stored in the sensor module. Accordingly, it is not necessary that the data processing circuit contained in the analyzer module xe2x80x9cseesxe2x80x9d the type of sensor involved and its individual correction algorithm, thus making it possible to operate totally differing types of sensors with a single, uniform analyzer module.
Initializing the sensor module is done, without the assistance of the analyzer module, on the basis of the configuration data stored in the sensor module. In the same way the sensor-specific data needed for digitally processing in the analyzer module together with the program code needed for this purpose and in the further course the measurement data to be processed are transferred by the analyzer module from the sensor module to the analyzer module without needing to be requested. Thus each data transfer is exclusively in the direction from the sensor module to the analyzer module, this being the reason why the digital interface between the two modules is a unidirectional serial interface permitting DC decoupling by simple means. In the opposite direction only the power supply of the sensor module from the analyzer module as well as, where necessary, transfer of a clock signal take place; these single-ended connections likewise permitting simple means of DC decoupling.